The present invention relates to a testing apparatus of strength.
A complex loads acts, repetitively, upon the transportation equipment, such as, a vehicle or a railway, etc., construction machinery, such as, a power shovel or a dump truck, etc., and/or the structure system of a natural energy power generating system, such as, for the wind-power generation or the wave-power generation, when operating, because of the various reasons thereof. This complex repetitive load is so-called a multi-axes repetitive load, changing amplitude in the waveform of the load with an elapse of time, as well as, changing a direction of the load, and may cause fatigue failure on such machines, as was mentioned above. For the purpose of avoiding such fatigue failure therefrom, it is important to fully understand a phenomenon of the fatigue to the multi-axes repetitive load. For such purpose as was mentioned above, multi-axes strength testing machines are invented and/or developed, for enabling a fatigue test on the multi-axes repetitive load.
The most general multi-axes strength testing machine is an apparatus having the structure, i.e., applying two (2) axes loads, such as, an axial direction load (e.g., a tensile/compressive load) and a torsion load, upon one end of a test piece having a rod-like or cylinder-like shape, while hold the other end thereof fixedly. Comparing to the other multi-axes strength testing machines having two (2) or more pieces of testing axes, which will be mentioned later, this type of multi-axes strength testing machine has only one (1) piece of a testing axis. This type of multi-axes strength testing machine has two (2) sets of actuators, such as, a translatory movement actuator to be used for the load in the axial direction, and rotary actuator to be used for the torsion load. Changing a waveform of the load in the axial direction and also a phase of a waveform of the torsion load enables a test under the multi-axes load (this will be called “non-proportional load”), i.e., chaining the direction of a main stress of the multi-axes stress generating on the test piece with an elapse of time. However, with this type of multi-axes strength testing machine, a condition of the multi-axes stress, which can achieved on the test piece, is limited. In more details, with this type of the apparatus, only a test is possible, under the condition of multi-axes stress where a ratio of main stress λ=σ3/σ1 obtained falls within a range of −1≦λ≦0, where σ1 is the maximum main stress and σ3 is the minimum main stress.
For the purpose of implementing a test exceeding the range of this main stress ratio is developed a multi-axes testing apparatus, having such structure as is written in the following Non-Patent Document 1. In this apparatus are disposed four (4) sets of translatory actuators, in a total thereof, each being so arranged to apply a load, respectively, to four (4) pieces of end portions of a cross, with respect to a test piece having almost cross-like shape. Two (2) sets of actuators are disposed so as to face to each other, thereby forming a 1-axis test structure, and two (2) sets of the 1-axis test structures enable the multi-axes fatigue test for the 2-axes load. The testing axis, passing through a center of the axes of the two (2) sets of the actuators facing to each other, comes across the axis of the other testing axis, which is constructed with other pair of actuators, at one point, and this point is coincident with a center of the test piece. With controlling the load applied by means of each actuator, it is possible to generate the condition of multi-stress condition at a central area of the test piece, including the center of the test piece therein. With is apparatus, it is possible to implement the test under the multi-stress condition mentioned above, i.e., within the range of the main stress −1≦λ≦0, however, in relation with such non-proportional load, as was mentioned above, only a part of the non-proportional load can be made. Also, because the two (2) sets of actuator build up the 1-axis test structure, there is a necessity of controlling the actuators facing to each other, at high accuracy, for maintaining the center of the test piece at the crossing point of the testing axes.
In the following Patent Document 1 is disclosed an apparatus, including three (3) or more sets of the 1-axis test structures, each for use of a mechanical load, and comprising a magnetic characteristic measurement means for a magnetic material. With this apparatus, it is possible to estimate the magnetic characteristic of the magnetic material under an arbitrary multi-stress condition. The testing axes, staying by three (3) or more pieces corresponding to the three (3) or more sets of the 1-axis test structures, cross one another at one (1) point, and the cross point thereof lies within a central area of the test piece. By means of a stress applying means, it is possible to generate the multi-stress condition within the central area of the test piece. With such structure of that apparatus, as is shown in this patent, it is possible to achieve the multi-stress condition within the range, where the main stress ratio lies in the range −1≦λ≦0, and also to direct the main stress of the multi-stresses into an arbitrary direction. The test piece has a shape or configuration, extending end portions thereof, radially, from the center of the test piece, fitting to the number of the testing axes and the directions of the axes. As an embodiment of the Patent Document is shown the structure of the apparatus, which provides a load means (e.g., a weight or a hydraulic actuator) so as to act a tensile load and a compressive load upon the end portion of the test piece. This means that those two (2) sets of the actuators build up the 1-axis test structure, similar to that show in the Non-Patent Document 1.
In the following Patent Document 2 is disclosed a multi-axes universal testing apparatus, comprising plural numbers of 1-axis test structures, similar to that show in the Patent Document 1. The apparatus is so constructed that the testing axes, being provided by the number same to that of those 1-axis test structures, cross a certain one (1) point. Since electromotive actuators are provided on both ends of each axis, this apparatus has the structures, being same to that shown in the Non-Patent Document 1, judging from a viewpoint that the two (2) sets of actuators build up the 1-axis test structure. This apparatus, similar to that show in the Patent Document 1, is able to achieve the multi-stress condition within the range of −1≦λ≦0, in the main stress ratio, and also to direct the main stress of the multi-axes stresses into an arbitrary direction.